What Controls Your Heart?

The answer to that question is a little more complicated than you may think. The heart is unique in that it is made up of muscle that is slightly different from the rest of the muscles in your body. Any cell in the heart can initiate contraction, independent of the rest of the heart. This is a form of protection for the heart to keep it beating if the nervous system fails to initiate contraction or if there is a block in electrical current through the heart. Even though the heart cells can contract without stimulation, the normal contraction pattern of the heart follows a coordinated pattern that starts with the “pacemaker” cells and allows the heart to contract in a synchronized, efficient manner. The pacemaker also set the speed in which your heart contracts. They are affected by the autonomic nervous system (maintains homeostasis in the body), which can increase or decrease speed of contraction.

The autonomic nervous system has two parts: the sympathetic and the parasympathetic. The sympathetic nervous system increases the heart rate and the force of contraction (think adrenaline, fight or flight response). The parasympathetic nervous system (also referred to as vagal tone) decreases the heart rate and force of contraction. Under normal, healthy conditions the parasympathetic system has more influence on the heart, especially in athletes who have slow resting heart rates.

One way to measure the health of your heart is to see how well it can react to the change in nervous system control. Recent studies have shown that patients with coronary artery disease have much less variability in the heart rate during simple tasks such as breathing, and greater heart rate variability has been shown to provide protection against arrhythmias and coronary heart disease. A greater heart rate reserve (the difference between resting and maximum heart rate) has been linked to heart health and a longer life expectancy. Though best tested with the help of a health professional, you can test this at home with a heart rate monitor. Measure your resting heart rate, lying down preferably in the morning before you eat or consume caffeine. Record this number; it should be between 60-100 beats per minute (less if you are physically fit). Recording heart rate max is more difficult and the calculation of 220 minus your age can be used as an estimate if maximal exercise is not possible. Another important test that can measure heart health is observed during recovery (in the minutes after exercise). The healthier heart can return to resting state faster than the diseased heart. To determine this yourself, measure your peak heart rate during exercise and then measure again during the two minutes post exercise. A normal recovery is a reduction of 20-30 beats per 60 seconds. If your heart does not decrease by 12 beats in the first minute, you should speak to your doctor.

To improve the health of your heart, increase your fitness level by increasing your regular aerobic exercise and control your weight with a sensible diet.

References:

Kestin, I. Control of Heart Rate. Physiology, issue 3 (1993) Article 3: Page 1
Airaksinen, K.. Impaired vagal heart rate control in coronary artery disease. British Heart Journal, 1987 December; 58(6): 592-597.

Ramaekers, D. Heart rate variability and heart rate in healthy volunteers. 1998, October; 19(9): 1334-1341.
Cole, C. Heart rate recovery immediately after exercise as a predictor of mortality. 1999, October; 341(18) 1351-1357.